fix(contracts): fix an index error in assets exchange

 Before this fix, a reverse asset exchange after a forward asset exchange process will report an index error because the confirm function is called after redeem but is not after init.

feat(*): use secp256k1 for signature verification

feat(*): add asset exchange contract

feat(client): replace native go plugin mechanism with grpc plugin

with grpc plugin

feat(Dockerfile): add dockerfile to build pier with fabric plugin

fix(*):fix deploy contracts fail

build(*): add contracts zip

Refactor/update fabric lib and new ibtp payload

update fabric from 1.4.6 to 2.0.1

update dependency version

feat(example): broker rollback with unique id

broker chaincode need to rollback according to a unique id instead of params passed from outside.

chore(go.mod): update package

update spf13/pflag package to be consistent with pier

chore(*): add test cover and workflow in github

1. add test cover for coverage report in workflow
2. add workflow for github action

chore(*): update bitxhub sdk and kit version

1. remove some unused code
2. add .golangci.yml for linter rule
3. add make prepare command

Bump bitxhub sdk and kit version to v1.0.0-rc1

chore(readme): add basic descriptions